HTML whitespace: spaces before and after <br>

Question

I am trying to better understand the HTML whitespace processing model. Right now I'm comparing two HTML snippets:

<div>a <br>z</div>

and

<div>a<br> z</div>

The first snippet, when renered, yields two lines: "a " and "z" (So the first line has a trailing space.)

The second snippet yields two lines: "a" and "z". There is no leading space on the second line.

My question is: why? I'm currently using this http://www.w3.org/TR/CSS2/text.html#white-space-model as a reference. It states

1. If a space (U+0020) at the beginning of a line has 'white-space' set to 'normal', 'nowrap', or 'pre-line', it is removed.
2. All tabs (U+0009) are rendered as a horizontal shift that lines up the start edge of the next glyph with the next tab stop. Tab stops occur at points that are multiples of 8 times the width of a space (U+0020) rendered in the block's font from the block's starting content edge.
3. If a space (U+0020) at the end of a line has 'white-space' set to 'normal', 'nowrap', or 'pre-line', it is also removed.
4. If spaces (U+0020) or tabs (U+0009) at the end of a line have 'white-space' set to 'pre-wrap', UAs may visually collapse them.

A naive reading of this would indicate that, since a space that the beginning or end of a line is to be removed (when 'white-space' is 'normal'), the first of my snippets ought to result in no trailing space. But that isn't the case.

So what's going on?

My current theory is that the <br> is secretly counted as a "character" which, in the first snippet, prevents the trailing space from being at the "end" of its line. But I really have no idea.

EDIT: To be clear, I know how to use   to create spaces at will. My question is about what rule (with regard to some spec) induces the above behavior.

Answer 1

Good question! I've confirmed the behavior in both Chrome and Firefox, and confirmed that it has nothing to do with <br>, as it's also triggered by an ordinary linebreak in white-space: pre-line conditions:

<div style="white-space:pre-line">a 
z</div>

I've sent an email to the list asking for clarification on this issue, and inquiring whether we should change the spec to match implementations, or file bugs on browsers to match the spec.